1. Field of the Invention
The present invention relates to a screening technique of semiconductor integrated circuit devices, e.g., Large-Scale Integrated circuit devices (LSIs). More particularly, the invention relates to a method of and an apparatus for screening semiconductor integrated circuit devices that screen out faulty devices (i.e., LSIs with some early failure), and a computer program product having a computer readable medium and a computer program recorded thereon that performs the method.
2. Description of the Related Art
Conventionally, the xe2x80x9cburn-inxe2x80x9d test or procedure has been well known and actually performed as a method of screening out defective LSIs with some early failure. This test or procedure is explained in detail, for example, in a book entitled xe2x80x9cIntegrated Circuit Quality and Reliabilityxe2x80x9d written by Eugene R. Hnatek, pp. 719-720. This is a method to deliberately apply electrical stress to LSIs to be tested in a high-temperature environment, thereby making temperature-dependent potential failures obvious in a comparatively short period of time. This is carried out to screen out faulty LSIs with some potential failure in an early stage, thereby improving the reliability of LSIs.
As explained above, the burn-in test is one of the accelerated tests capable of eliciting the potential failure of LSIs in a comparatively short period of time. However, this test has a disadvantage that it may take a long time such as several hundreds or several thousands hours to complete the test when the type of failure modes to be elicited is time-consuming and/or the required level of reliability is high. Thus, there is the need to make it possible to screen out defective or faulty LSIs with some potential failure in a sufficiently short period of time.
Moreover, the burn-in test has a danger that the potential failure of LSIs is unable to be found or observed, which is due to the following reason. Specifically,. potential defects or failures existing in LSIs degrade gradually with time due to applied stresses in the burn-in test. These defects or failures are not found or observed unless they are completely elicited during the test. Thus, there is a possibility that the potential defects or failures in LSIs are not found even if the test is finished.
Accordingly, an object of the present invention is to provide a method of screening semiconductor integrated circuit devices that makes it possible to screen out faulty devices before potential failure existing therein through a burn-in test is elicited, and a computer program product that performs the method.
Another object of the present invention is to provide an apparatus for screening semiconductor integrated circuit devices capable of screening out faulty devices before potential failure existing therein is elicited through a burn-in test.
Still another object of the present invention is to provide a method of screening semiconductor integrated circuit devices that screens out faulty devices with potential failure in a short period of time, and a computer program product that performs the method.
A further object of the present invention is to provide an apparatus for screening semiconductor integrated circuit devices capable of screening out faulty devices with potential failure in a short period of time.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to a first aspect of the present invention, a method of screening semiconductor integrated circuit devices is provided This method comprises the steps of:
(a) supplying a specific power supply voltage to semiconductor integrated circuit devices to be tested while applying a specific test signal to the devices at a specific period;
(b) observing power supply currents of the devices caused by the power supply voltage and the test signal;
(c) generating sets of power spectrum data of the power supply currents of the devices corresponding to the test signal;
(d) generating distributions of the sets of power spectrum data of the power supply currents; and
(e) judging whether or not the distributions of the sets of power spectrum data of the power supply currents are equal to or greater than a specific reference value;
wherein when the distribution of the set of power spectrum data of the power supply current of one of the devices is equal to or greater than the reference value, the device in question is regarded as a faulty one,
With the method according to the first aspect of the present invention, a specific power supply voltage is supplied to semiconductor integrated circuit devices to be tested while applying a specific test signal to the devices at a specific period in the step (a). Then, power supply currents of the devices caused by the power supply voltage and the test signal are observed in the step (b). Sets of power spectrum data of the power supply currents of the devices corresponding to the test signal are generated in the step (c). Distributions of the sets of power spectrum data of the power supply currents are generated in the step (d). Finally, whether or not the distributions of the sets of power spectrum data of the power supply currents are equal to or greater than a specific reference value is judged in the step (e).
Thus, when the distribution of the set of power spectrum data of the power supply current of one of the devices is equal to or greater than the reference value, the device in question is regarded as a faulty or good one. As a result, faulty devices can be screened out before potential failure existing therein through a burn-in test is elicited.
Moreover, since no burn-in test is necessary, faulty devices with potential failure can be screened out in a short period of time.
In a preferred embodiment of the method according to the first aspect, further comprising a step of performing a burn-in test for the devices prior to the step (a). In this embodiment, there is an additional advantage that faulty devices can be screened out more accurately than the case where no burn-in test is carried out prior to the step (a).
In another preferred embodiment of the method according to the first aspect, the test signal includes a single set of test patterns, or sets of test patterns that are consecutively arranged with time, or sets of test patterns that are consecutively arranged with time at specific intervals.
According to a second aspect of the present invention, another method of screening semiconductor integrated circuit devices is provided. This method comprises the steps of:
(a) supplying a specific power supply voltage to semiconductor integrated circuit devices to be tested while applying a specific test signal to the devices at a specific period;
(b) observing power supply currents of the devices caused by the power supply voltage and the test signal;
(c) generating sets of power spectrum data of the power supply currents of the devices corresponding to the test signal;
(d) generating distributions of the sets of power spectrum data of the power supply currents before a burn-in test;
(e) performing the steps (a) to (d) while performing a burn-in test for the devices after the step (d), generating distributions of the sets of power spectrum data of the power supply currents during the burn-in test;
(f) performing the steps (a) to (d) after the burn-in test is completed in the step (e), generating distributions of the sets of power spectrum data of the power supply currents after the burn-in test;
(g) generating distribution change rates of power spectrum data of the power supply currents based on the distributions of the sets of power spectrum data of the power supply currents obtained in the steps (d), (e), and (f); and
(h) judging whether or not the distribution change rates of power spectrum data of the power supply currents generated in the step (g) are equal to or greater than a specific reference value;
wherein when the distribution change rate of power spectrum data of the power supply current of one of the devices is equal to or greater than the reference value, the device in question is regarded as a faulty one.
With the method according to the second aspect of the present invention, before the burn-in test, the steps (a) to (d) are tarried out, generating the distributions of the sets of power spectrum data of the power supply currents before a burn-in test. Thereafter, the steps (a) to (d) are performed in the step (e) while performing a burn-in test for the devices after the step (d), generating the distributions of the sets of power spectrum data of the power supply currents during the burn-in test. Further, the steps (a) to (d) are performed after the burn-in test is completed in the step (e), generating the distributions of the sets of power spectrum data of the power supply currents after the burn-in test. Finally, the distribution change rates of power spectrum data of the power supply currents are generated in the step (g) based on the distributions of the sets of power spectrum data of the power supply currents obtained in the steps (d), (e), and (f).
The good devices have small time-dependent change rates of the power spectrum data, because they include no potential fault or defect and therefore, they scarcely degrade in performance even after the burn-in test is completed. In contrast, the faulty devices have large change rates of the power spectrum data, because the faulty devices include some potential fault or defect and therefore, they distinctly degrade in performance after the burn-in test is completed.
Accordingly, by judging whether or not the distribution change rates of power spectrum data of the power supply currents generated in the step (g) are equal to or greater than a specific reference value in the step (h), the device in question can be found as a faulty or good one.
In a preferred embodiment of the method according to the second aspect, the test signal includes a single set of test patterns, or sets of test patterns that are consecutively arranged with time, or sets of test patterns that are consecutively arranged with time at specific intervals.
According the a third aspect of the present invention, an apparatus for screening semiconductor integrated circuit devices is provided. This apparatus comprises:
(a) a test power supply for generating a power supply voltage applied to semiconductor integrated circuit devices to be tested;
(b) a test signal generator for generating a test signal supplied to the devices;
(c) a spectrum analyzer for observing power supply currents of the devices caused by the power supply voltage and the test signal and for generating sets of power spectrum data of the power supply currents of the devices corresponding to the test signal;
(d) a data storage for storing the sets of power spectrum data of the power supply currents of the devices; and
(e) a data analyzer for generating distributions of the sets of power spectrum data of the power supply currents and for judging whether or not the distributions of the sets of power spectrum data of the power supply currents are equal to or greater than a specific reference value;
wherein when the distribution of the set of power spectrum data of the power supply current of one of the devices is equal to or greater than the reference value, the device in question is regarded as a faulty one.
With the apparatus according to the third aspect of the present invention, the method of the first or second aspect of the invention can be carried out. Therefore, there are the same advantages as those in the method of the first aspect of the invention.
According to a fourth aspect of the present invention, a computer program product having a computer readable medium and a computer program recorded thereon is provided The computer program is operable to screen semiconductor integrated circuit devices. This product is to perform the method of the first aspect of the invention.
This product comprises:
(a) code that supplies a specific power supply voltage to semiconductor integrated circuit devices to be tested while applying a specific test signal to the devices at a specific period;
(b) code that observes power supply currents of the devices caused by the power supply voltage and the test signal;
(c) code that generates sets of power spectrum data of the power supply currents of the devices corresponding to the test signal;
(d) code that generates distributions of the sets of power spectrum data of the power supply currents; and
(e) code that judges whether or not the distributions of the sets of power spectrum data of the power supply currents are equal to or greater than a specific reference value;
wherein when the distribution of the set of power spectrum data of the power supply current of one of the devices is equal to or greater than the reference value, the device in question is regarded as a faulty one.
According to a fifth aspect of the present invention, another computer program product having a computer readable medium and a computer program recorded thereon is provided, The computer program is operable to screen semiconductor integrated circuit devices. This product is to perform the method of the second aspect of the invention.
This product comprises:
(a) code that supplies a specific power supply voltage to semiconductor integrated circuit devices to be tested while applying a specific test signal to the devices at a specific period;
(b) code that observes power supply currents of the devices caused by the power supply voltage and the test signal;
(c) code that generates sets of power spectrum data of the power supply currents of the devices corresponding to the test signal;
(d) code that generates distributions of the sets of power spectrum data of the power supply currents before a burn-in test;
(e) code that performs the steps (a) to (d) while performing a burn-in test for the devices after the step (d), generating distributions of the sets of power spectrum data of the power supply currents during the burn-in test;
(f) code that performs the steps (a) to (d) after the burn-in test is completed in the step (e), generating distributions of the sets of power spectrum data of the power supply currents after the burn-in test;
(g) code that generates distribution change rates of power spectrum data of the power supply currents based on the distributions of the sets of power spectrum data of the power supply currents obtained in the steps (d), (e), and (f); and
(h) code that judges whether or not the distribution change rates of power spectrum data of the power supply currents generated in the step (g) are equal to or greater than a specific reference value;
wherein when the distribution change rate of power spectrum data of the power supply current of one of the devices is equal to or greater than the reference value, the device in question is regarded as a faulty one.